1. Field of the Invention
The present invention relates to a power line detection system for air borne vehicles such as helicopters and light aircraft. More specifically, it relates to a short-range, radio frequency transmitting-receiving system that provides both visual and audio warnings to the pilot of a helicopter or light aircraft of an up-coming power transmission line complex.
2. Description of Related Art
The major cause of helicopter fatalities in the United States is a "wire strike". This is defined as a helicopter flying into a suspended power transmission line and subsequently crashing. To date, the most common technique used to warn lowflying aircraft of this danger is a visual one; colored balls are placed on the transmission lines themselves. Strobe lights are sometime used. These method are ineffective in poor weather.
Power transmission lines and overhead cables and wires, which represent the smallest obstacles, are not detectable by conventional microwave radar owing to their small size, and the specular nature of the return signal at the microwave frequencies. Thermal imaging systems are also inadequate since wires are often at the same temperature as the background or are below the resolution limit of these systems. Accident statistics indicate that the high damage incidents and hence high cost are attributable to collisions with power cables since these are the strongest of all cables. See U.S. Pat. No. 4,902,126.
One approach, using radar to detect obstacles in the flight plane, is to discriminate against terrain echos on the basis of vertical antenna directivity, whereby echos from obstacles outside the flight plane are attenuated compared to those close to the flight plane. Unfortunately, directivity in simple radar systems requires large antenna apertures, which are heavy and not compatible with the aerodynamics of airborne vehicles. However, it is well known that a large synthetic aperture can be generated by processing signals received while a relatively small physical antenna is transported through space. This principle is exploited in some airborne radars in which special signal processors use the Doppler history of reflections from terrain objects imparted by aircraft motion to enhance the horizontal resolution of the physical antenna. These techniques fail when the airborne vehicle velocity approaches zero.
It would be advantageous if there were an all-weather, continuously-operating system for alerting helicopter and light aircraft pilots that a potential power line hazard exists in their immediate area. The present invention provides such a system.